1. Field of the Invention
The present invention relates to a grasping device, particularly, to a grasping device suitable for such grasping devices as that usable for grasping and taking out at a time many small molded articles or works which molded at a time by an injection molding machine, or that usable, in insert-molding technique integrally molding a thin work and synthetic resin, for grasping the thin work and inserting it into a mold in an injection molding machine.
2. Description of the Prior Art
Conventionally, in a synthetic resin molding technology, particularly, in a system of taking out molded works which system is called “a lot of articles take-out system” and grasps and takes out at a time many small molded articles molded at a time, a grasping device 50 shown in FIGS. 9, 10 and 11 is employed.
In FIGS. 9, 10 and 11, the grasping device 50 is provided for grasping and taking out at a time many small molded articles (not shown) molded (produced) at a time by an injection molding machine (a producing facility) 51. The grasping device 50 is mounted at the tip of a rotating arm 52a of a molded article take-out machine (a conveying means) 52 which conveys many small molded articles from a work-grasping position (see the solid line in FIG. 11) opposite to an opened mold 51a of an injection molding machine 51 to a work-releasing position (for example, see the two-dots chain line in FIG. 11) outside the injection molding machine 51.
The grasping device 50 is in the form of a frame in a square shape in a front view and made of a metal plate or hard synthetic resin plate having a small thickness (t). The grasping device 50 comprises a base 53 mounted to an utmost end of a rotating arm 52a, and a grasping part 54 provided extending from the base 53. The grasping part 54 consists of: an upper side part 54a and a lower side part 54b facing and being paralleled to each other; a longitudinal side part 54c which extends vertically to connect the ends at the base 53 side of the upper and the lower side parts 54a and 54b; another longitudinal side part 54d which extends vertically to connect the utmost ends of the upper and the lower side parts 54a and 54b; and a pair of longitudinal frame parts 54e each extending vertically to connect the upper and the lower side parts 54a and 54b between the longitudinal side parts 54c and 54d. 
Mounted on the side parts 54a through 54d and the pair of longitudinal frame parts 54e (separately at specific predetermined positions corresponding to specific positions where many small molded articles are molded/produced by the injection molding machine 51 at a time) are many adsorbing pads 55 for grasping the many small molded articles at a time. The adsorbing pads 55 communicate with suction and air-feed pipes 57 through suction and air-feed passages 56 formed inside the side parts 54a through 54d and the pair of longitudinal frame parts 54e. And the suction and air-feed pipes 57 are connected to a suction and air-feed means (not shown) through a suction and air-feed switching valve (not shown).
With the grasping device 50 having the foregoing structure being in the state of positioned at the work-release position illustrated by the two-dots chain line in FIG. 11, the rotating arm 52a of the molded article take-out machine 52 is rotated to move the grasping device 50 to a work grasping position (as illustrated by the solid line in FIG. 11) opposing to the opened mold 51a of the injection molding machine 51. The grasping device 50 is further caused to approach the mold 51a, particularly, a movable mold 51a. Then, the suction/air-feed switching valve is switched over to cause the suction means to communicate with the suction/air-feed pipe 57, thereby causing the suction/air-feed pipe 57 and suction/air-feed passage 56 to be subject to negative pressure, so that the many small molded articles molded by the injection molding machine 51 at a time are grasped by the large number of adsorbing pads 55 at a time.
When the grasping device 50 completes adsorbing and grasping the many small molded articles, the rotating arm 52a is revolved in a reverse direction to cause the grasping device 50 to be moved to the work-release position outside the injection molding machine 51 (that position illustrated by the two-dots chain line in FIG. 11). Then, the suction/air-feed switching valve is switched over to cause the air-feed means to communicate with a plurality of the suction/air-feed pipes 57, whereby causing the suction/air-feed pipes 57 and the suction/air-feed passage 56 to have positive pressure, so that the many small molded articles are released, followed by properly collecting/gathering them.
In the meantime, a grasping device employed in a system, which system grasps a thin work and inserts it into a mold in an injection molding machine, in the “insert molding” technique integrally molding the thin work and synthetic resin, is described in Japanese Patent No. 2958989 (Patent Document 1).
As shown in FIGS. 12 and 13, the grasping device 60 described in the patent document 1 is in the shape of a rectangular frame in a front view substantially the same in form as of a thin work such as a label and is made of metal or hard synthetic resin. The grasping device 60 comprises a rectangular base 61 integrally mounted at the rear side, and a grasping part 62, the rectangular base 61 being connected at its one end to an arm 64 of a right-angle coordinate system robot (a conveying means) 63.
The grasping part 62 consists of: an upper side part 62a and a lower side part 62b facing and being paralleled to each other; a longitudinal side part 62c which extends vertically to connect the ends at the arm 64 side, i.e., the base side, of the upper and the lower side parts 62a and 62b; another longitudinal side part 62d which extends vertically to connect the utmost ends of the upper and the lower side parts 62a and 62b; and a transverse frame part 62e extending horizontally to connect the two longitudinal side parts 62c and 62d between the upper and the lower side parts 62a and 62b. 
The side parts 62a through 62d and the transverse frame part 62e are provided with many vacuum holes 65 each apart at a predetermined interval to one another. The vacuum holes 65 communicate with an air chamber 66 formed at the base 61 side at a mounting interface between the base 61 and the grasping device 62. The air chamber 66 communicates with a suction/air-feed pipe 67 which is connected with a suction/air-feed means (not shown) through a suction/air-feed switching valve which not shown. An adsorbing pad 55 explained in FIG. 9 may be mounted to the respective opening of the many vacuum holes 65.
In the grasping device 60 having the above structure, the grasping device 60 is moved, by the robot 63, to an escape position of a work (label) magazine, so that the grasping part 62 is abutted against the work to be stopped. Then, the suction/air-feed switching valve is switched over to cause the suction means to communicate with the suction/air-feed pipe 67, whereby causing the suction/air-feed pipe 67, air chamber 66 and the many vacuum holes 65 to be subject to negative pressure, so that the work is adsorbed and grasped by the grasping part 62.
Next, the robot 63 causes the grasping part 62 of the grasping device 60 to approach (and stop there) a front mold (not shown) of an opened mold in an injection molding machine (not shown). Then, the suction/air-feed switching valve is switched over to cause the air-feed means to communicate with the plurality of the suction/air-feed pipes 67, whereby causing the suction/air-feed pipes 67, air chamber 66 and the many vacuum holes 65 to be subject to positive pressure, so that the work is released and inserted into the front mold.
In the meantime, the grasping device 50, which grasps at a time the many small molded articles as explained in FIGS. 9, 10 and 11, is moved from the work-release position illustrated by two-dots chain line in FIG. 11 to the work-grasping position illustrated by solid line, so that due to inertia occurring there upon stoppage of the grasping device 50 the grasping part 54 of the grasping device 50 has vibration mainly in the direction of thickness (t). The vibration in the thickness (t) direction is concluded to be magnified due to a larger weight of the grasping part's utmost end side most away from the base 53 since the grasping part 54 is provided at its utmost end with the second longitudinal side part 54d. 
When the grasping part 54 vibrates in the thickness (t) direction in this way, the precise adsorbing and grasping the many small molded articles by the many adsorbing pads 55, in other words, an accurate adsorbing and grasping of the molded articles by the grasping part 54, is spoiled, deteriorating precision of grasping of the molded articles by the grasping device 50. Hence, it is necessary to refrain from grasping the small molded articles during the time interval from the stoppage of the grasping device 50 at the work-grasping position to decay and disappearance of the vibration in order to avoid lowering of precision in grasping the molded articles. As a result, a cycle time of grasping the molded articles by the grasping device 50 is inevitably longer, which causes lowering of an efficiency of molding by the injection molding machine.
Meanwhile, the grasping device 60 explained in FIGS. 12 and 13, which grasps a thin work and inserts it into the mold in the injection molding machine, does have vibration mainly in the direction of thickness due to inertia arising when the grasping device 60 is moved to an escape position of a work (label) magazine by means of the robot 63 to cause the grasping part 62 to abut against the work and stop there, and also due to inertia occurring when the grasping part 62 of the grasping device 60 is caused, by the robot 63, to approach (and stop there) the front mold of the opened mold in the injection molding machine. The vibration in the thickness direction is concluded to be magnified due to a larger weight of the grasping part's utmost end side most away from the one longitudinal side part 62c, i.e., an end of the base side since the grasping part 62 is provided at its utmost end with the other longitudinal side part 62d. 
When the grasping part 60 vibrates in the thickness direction in this way, the precise adsorbing and grasping of the work by the many vacuum holes 65 is spoiled, deteriorating precision of grasping of the work by the grasping device 60 and also lowering precision of inserting of the work. Hence, it is necessary to refrain from grasping the work during the time interval from the stoppage of the grasping device 60 at the escape position of the work (label) magazine to the decay and disappearance of the vibration in order to avoid lowering of precision in grasping the work. Besides, it is necessary to refrain from releasing the work during the time interval from the approaching and stoppage of the grasping part 62 of the grasping device 60 with respect to the front mold to the decay and disappearance of the vibration in order to avoid lowering of precision of inserting the work. As a result, a cycle time of inserting the work by the grasping device 60 is inevitably longer, which causes lowering of an efficiency of forming by an in-mold forming machine.